BCECE Engineering BCECE Engineering Solved Paper-2011

  • question_answer
    If \[(1+tan\theta )(1+tan\phi )=2,\]then \[(\theta +\phi )\]is equal to

    A) \[{{30}^{o}}\]                                        

    B)         \[{{45}^{o}}\]                       

    C)        \[{{60}^{o}}\]                                        

    D)        \[~{{75}^{o}}\]

    Correct Answer: B

    Solution :

    We have, \[(1+tan\theta )(1+tan\phi )=2\] \[\Rightarrow \] \[1+\tan \theta +\tan \phi \text{+}\,\text{tan}\theta \text{.tan}\phi \text{=}\,\text{2}\] \[\Rightarrow \] \[\tan \theta +\tan \phi =1-\tan \theta .\tan \phi \] \[\Rightarrow \]    \[\frac{\tan \theta +\tan \phi }{1-\tan \theta .\tan \phi }=1\] \[\Rightarrow \]    \[\tan (\theta +\phi )=tan\pi /4\]                 \[\theta +\phi \,=\pi /4={{45}^{o}}\]


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